CHM 101
Sinex
Molecular Polarity - How?
Molecular Polarity
Predicting and Understanding
the Behavior of Molecules
PGCC CHM 101 Sinex
Lewis dot structure à geometry à bond
polarity (∆EN) and lone pairs à how is
the charge distribution – symmetrical or
asymmetrical?
Electrostatic potential map using Chime
N2
HCl
Spartan 02
Chime activity - Click here
Molecular Polarity - Why?
An experimental measurement
Interactions with other molecules and
physical properties such as boiling point,
surface tension, and solubility
The dipole moment, µ, is given by
Intramolecular interactions – within
molecule such as proteins
Reaction mechanisms – where attacked
Measurement: Dipole Moment
µ = Qd
where Q is the charge
and
d is the separation distance of the charge
The unit is the debye, D.
Measurement: Dipole Moment
-
No voltage applied on metal plates
δ- δ+
+
Voltage applied on metal plates
δ- δ+
1
CHM 101
Sinex
Dichloromethane, CH2Cl2
Dipole Moments
∆EN
Bond length
(pm)
µ (D)
HF
1.9
92
1.82
0.8
127
1.08
0.6
141
0.82
0.3
161
0.44
HCl
HBr
HI
Increasing polarity
Hydrogen
Halide
µcalc = 1.50 D
Spartan 02
A square planar complex - Pt(NH 3)2Cl2
Ammonia, NH3
É Cl-Pt-N = 80o
Polar or
Non-polar
É Cl-Pt-Cl = 101.4o
polar
µcalc = 1.85 D
Spartan 02
Spartan 02
Non-polar
Polar or non-polar molecules?
CCl2F2
HCN
SCl4F2
ICl3
BCl3
BrCl
2